of propagation man is best acquainted), may be produced artificially. But
the process by which their production is thus effected, is more properly a
natural than an artificial one. In speaking of truffle-grounds, he says
(quoting from Broome) "that whenever a plantation of beech, or beech and
fir, is made in the chalky districts of Salisbury Plain, after the lapse
of a few years truffles are produced, and that the plantations continue
productive for a period of from ten to fifteen years, after which they
cease to be so." No truffle spores were planted in these cases, but the
conditions of the soil, interlaced by the roots and shaded by the branches
of the young beech trees, or the beech and fir, became favorable for the
development of truffle "germs," and they made their appearance just as
mushrooms do in caves and other places, where artificial beds are made and
chemically balanced for their development and growth. And the reason why
they disappeared, after a period of ten or fifteen years, was simply
because the proper nutriment of the soil was exhausted, and not in
consequence of its being too deeply shaded by the growing trees. One
uniform rule would seem to govern in the culture of this much-coveted
fungus. Wherever the necessary environing conditions obtain, they
_appear_, and wherever these conditions fail, they _disappear_,
notwithstanding the most persistent efforts to save them by watering the
soil with fresh infusions of the plant. In proof of this, one form of
truffle (_Tuber A|stivum_) appears under beech trees, another form (_Tuber
macrosporum_) under oak trees, and still a third form (_Tuber brumale_)
under oaks and white poplars; showing that so slight a change in soil
conditions as that resulting from the presence of poplars among oaks,
produces a very material change in the character of the fungus--one
amounting to a specific difference in variety.

The process of artificially producing mushroom spores is a very simple
one, and may be easily followed. You have only to collect a quantity of